1. Field of the Invention
The present invention relates to a duplex printing apparatus, and more particularly to a paper feed apparatus for reversing a paper feed path for duplex printing.
2. The Related Art
A duplex printing apparatus includes a duplex printing master on which two sides of a sheet are printed in series. The sheet is printed by pressing a front side of the sheet against the duplex printing master through a paper feed apparatus. The other side of the sheet is printed by pressing a reverse side of the sheet against the duplex printing master through the paper feed apparatus. So the paper feed apparatus can achieve the reverse of the sheet.
Referring to FIG. 1, a conventional paper feed apparatus 700 includes a gate 710, an actuator 720, a transmission 730, a pickup device 740, a reversing device 750, a paper feed device 760.
Referring to FIG. 2 and FIG. 3, the actuator 720 comprises a pickup gear 721, an arm 722 and a pickup idler gear 723 which has a same angular speed with the pickup gear 721. The arm 722 mounted between the pickup gear 721 and the pickup idler gear 723 has a friction spring 724 that can cause a torque.
Refer to FIG. 4 and FIG. 5. When a sheet is fed to the paper feed device 760, the gate 710 is in a closed position while the arm 722 is pressed by the actuator 720. The pickup gear 721 is reversed following a motor while the sheet will leave the paper feed device 760, and then the torque caused between the pickup gear 721 and the arm 722 rises the arm 722 to make the gate 710 be in an open position. The sheet is fed to the paper feed device 760 through the reversing device 750 again to achieve duplex printing.
Based on the conventional art, the components of the paper feed apparatus 700 are too many to ensure the paper feed apparatus 700 working effectively. So, it would be desirable to provide a paper feed apparatus 700 that is of simple design and low cost.